1. Field of the Invention
The present invention in general relates to an oil mist prevention structure, in particular, to an oil mist prevention structure for encoder.
2. Description of Prior Art
The main purpose of a rotary encoder is to measure the rotary angles, which is comprehensively applied in automatic control system to provide the system with signals of angular positions, whereby a determination of control is made. For example, in a server motor for a driving purpose, the motor responsible for executing the position and speed orders sent out by the system is arranged an encoder on the shaft as a position sensor. By so doing, the positioning accuracy of the server motor is dependent on the resolution of the encoder. In general, the rotary encoder is mainly divided into two kinds: the magnetic encoder and the optical encoder.
Through magnetic force to generate impulse series as signals, a magnetic encoder is easily influenced by dust, oil mist and vapor, so its measuring resolution originated from sensing the variation of magnetic force is still low. On the other hand, by emitting parallel light beams passing through light and dark gratings on a glass disk to generate 0 and 1 signals, an optical encoder has a relatively high resolution for distinguishing and measuring purposes. However, this kind of encoder is more sensitive to the contamination caused by oil mist, vapor and dust.
As shown in FIG. 1, an optically rotary encoder mainly includes an encoding body 10a, a pair of oil-containing bearings 20a, a shaft 30a, a rotary disk 40a and a light acceptor 52a, in which the encoding body 10a is arranged specific components, such as, a light emitter 12a and a secondary encoding piece 20; the oil-containing bearings 20a are arranged in a central hole of the encoding body 10a; the shaft 30a penetrates the oil-containing bearing 20a; the light acceptor 52a is fixed onto the encoding body 10a to correspond to the light emitter 12a and the secondary encoding piece 13a. By so doing, the parallel light beams generated from the light emitter 12a passes through the rotary disk 40a and the fixedly secondary encoding piece 13a to reach the light acceptor 52a. The strength of the light beam generated from the light emitter 12a and received by the light acceptor 52a is varied differently according to the different positions of the rotary disk 40a. Through detecting the signal variation generated by the light acceptor 52a, the positional information can be obtained.
However, according to the optical encoder of most kinds of prior arts is usually arranged one to two pieces of oil-containing bearings 20a therein to enhance the smoothness and stability of the rotary disk 40a when rotating. But, the use of oil-containing bearing 20a will heat the lubricant to be vaporized into oil mist, which will contaminate the rotary disk 40a and the secondary encoding piece 13a during rotation. Or, when the encoder is operating, the lubricant of the bearing 20a will splash onto the rotary disk 40a or the secondary encoding piece 13a, causing the optical encoder outputting inferior or erroneous signals.
In addition, in current practice, most optical encoders use a cylindrical shaft 30a and are fixed onto the bearing 20a by adhesive by means of interfering cooperation. By so doing, when knocked and beaten by external force in axial direction, it is very likely that the shaft 30a generates a displacement to damage the encoder, which is a problem needed to be solved urgently.
Accordingly, after a substantially devoted study, in cooperation with the application of relative academic principles, the inventor has finally proposed the present invention designed reasonably to possess the capability to improve the drawbacks of the prior arts significantly.